The Asian economic crisis could undermine global efforts to control the killer disease tuberculosis, according to the World Health Organisation (WHO).

Over a half of all new cases of TB - the world's most deadly infectious disease - are in six Asian countries - Bangladesh, China, India, Indonesia, Pakistan and the Philipinnes.

They account for 4.5m of the 8m a year new cases of the respiratory disease.

The WHO fears economic crisis and an increase in poverty will create conditions which will help spread the disease.

And it believes cutbacks in health funding could undermine efforts to treat tuberculosis.

TB epicentre

Gro Harlem Bruntland, director general of the WHO, is urging governments to do all they can to back a global campaign against TB.

Gro Harlem Brundtland: 'our ability to control TB pivots on Asia'

"Our ability to control TB pivots on Asia - now the epicentre of the world," she said.

"If we cannot control TB in Asia, we will never stop TB globally."

She was speaking in a video-taped message sent to a four-day conference on lung disease starting in Bangkok, Thailand, on Monday.

The conference brings together over 1,000 experts from 90 countries and is the largest in Asia in a decade.

Daily drug programme

Around 3m people a year die of TB. Children can be vaccinated against the disease, but the vaccination wears off when they reach adulthood.

TB can be treated successfully, but patients are required to follow a six-month daily drug programme.

Many stop taking the drugs after a month or so as they start to feel better.

The poor are particularly likely to fall into this category as they may find it difficult to pay for the drugs.

This had led to the rise of drug-resistant strains of the TB bacilli.

TB is also linked to the virus that causes Aids. HIV attacks the body's immune system, making it less likely to be able to fight TB.

Dr Chris Dye of the WHO said: "The problem with TB is that many people are already infected with the baccilus that ultimately causes the disease.

"Under normal circumstances, most of those people will never develop the disease, but when HIV comes along their immune system is weakened and they have a much higher chance of develping TB as a result."

The WHO estimates that HIV will account for 14% of TB deaths by the year 2000.

Richard Bumgarner of the WHO's TB programme said HIV had caused TB in Africa to spiral out of control since the 1970s.

Asia was likely to see similar problems if urgent action was not taken.

"The HIV epidemic contributes to the TB burden (in Thailand) by 15 to 20% each year," he said.

"In the northern regions it contributes up to 30%."

Observation treatment

A WHO report, published on Monday, says the best way of reducing the spread of TB is to ensure people finish their course of treatment.

The most effective way is to set up a system to observe patients taking their drugs. It is known as Directly Observed treatment, Short-course and is being used in more than 100 countries.

The World Bank says it believes the system can save billions of dollars in the long term.

In China where it is used in several provinces, it is said to have led to a 95% increase in TB cure rates.

Chinese health officials are now seeking to expand the programme to cover the whole of China.

The WHO estimates it could save 2.3bn Thai dollars in the next 20 years.